Duplicates services/asterisk.sh (left untouched) into a DO-specific
variant: auto-detects the droplet's public IP/ID via the DO metadata
service, always assumes a public FQDN (no LAN/VLAN prompts), offers to
provision a matching DigitalOcean Cloud Firewall via doctl (never
touching one that's already attached), and documents droplet sizing,
firewall rules, and Sipnetic client setup in the generated README.
